(a) Field of the Invention
The present invention relates to a thermo-developable type diazo copying material which is also usable as a recording material.
(b) Description of the Prior Art
Thermo-developable type diazo copying materials are generally comprised of a substrate such as paper, film or the like and a photosensitive layer, formed thereon, which consists essentially of a diazo compound, a coupler and a color assistant. As the color assistant there is employed urea, sodium trichloroacetate or the like. The diazo copying materials of this type are each developed by heating at a high temperature of 150.degree. to 200.degree. C. The developing mechanism is designed to utilize alkali (ammonia gas or caustic soda) generated by heat decomposition. In order to achieve development at a low temperature such as 90.degree. to 130.degree. C., an attempt has been made to use higher fatty acid amides as the color assistant, and the developing mechanism used therefor is designed to utilize the phenomenon that the diazo compound and coupler are melted by heating and thus are activated.
In the conventional thermo-developable type diazo copying materials, however, the former copying materials are defective in that since development is effected at a high temperature as aforesaid, it is necessary to selectively employ a highly heat-resistant diazo compound. This is unfavorable for the formation of a high density image, because with diazo copying materials of this type, generally speaking, it is difficult to obtain a high density image as compared with dry diazo copying materials which are developed with ammonia gas. Further, a heating device adapted to maintain a high accuracy even at high temperatures is required, because if the temperature is not controlled within the limits of about .+-.10.degree. C., there will be caused insufficient development and changes in color tone. The copying machine unavoidably becomes expensive when such devices are used. The copying materials in the latter case, on the other hand, are defective in that development can be carried out at low temperatures but the preservability of the copying material itself (which will be called "raw preservability" hereinafter) deteriorates with time.
U.S. Pat. No. 3,202,510 discloses a thermo-developable type diazo copying material in which an alkali generating agent such as urea is employed as a color assistant so that color may be formed only when the material is heated and a coupler is encapsulated with a wax-like substance such as microcrystalline wax. However, this copying material has poor color formability.
Methods using thermo-developable type diazo copying materials are surely advantageous in that dry copies can be obtained, and the copying machines used therefor can be made compact due to the simplicity of the developing sections but they cannot become the leading diazo copying processes due to the aforesaid defects.